The present invention relates generally to pumping devices, and more particularly to a fluid pump and ink jet print head using a temperature gradient across a multiple fluid interface to generate fluid motion.
Various pumps are used in printers to pump ink out of a nozzle and onto a print medium. For example in a bubble jet printer, the ink in a channel is heated to a boil to create a bubble until the pressure ejects a droplet of the ink out of a nozzle. The bubble then collapses as the heating element cools, and the resulting vacuum draws fluid from a reservoir to replace the ink that was ejected from the nozzle. Such thermal technology requires a cooling period between ejecting successive droplets from a nozzle and thus has speed limitations. Also, such thermal technology cannot be used to pump fluids that are adversely affected by boiling.
Piezoelectric pumps, such as that disclosed in U.S. Pat. No. 5,224,843, have a piezoelectric crystal in the fluid channel that flexes when an electric current flows through it to force a drop of fluid out of a nozzle. Piezoelectric technology is faster and provides more control over the fluid movement as compared to thermal technology. Also, because the fluid to be pumped is not heated significantly, the fluid can be selected based on its relevant properties rather than its ability to withstand high temperatures. However, piezoelectric microscale pumps are complex and thus expensive to manufacture.
Further, fluid pumps are often required in various applications in which a high degree of control is required and high temperatures are to be avoided. For example, pumps can be used in biological heat-pipe type devices, devices which administer small doses of fluid into a larger stream of fluid, devices which pump various solutions that are unstable when boiled, devices which pump biological materials and other materials that must be maintained at a constant temperature, and other generic pumping applications.
It is well known to utilize the xe2x80x9cMarangoni type effectxe2x80x9d to pump fluids. The Marangoni type effect refers to a phenomenon that occurs at the interface of two immiscible fluids when the surface tension on the interface is not constant, i.e. has a gradient. In particular, a fluid flow is established along the fluid interface in the direction of increasing surface tension. Successive layers of the fluid below the interface are dragged along due to the viscosity of the fluid to establish a general current in the fluid in the direction of the Marangoni type flow. The surface tension gradient can be established by a temperature gradient along the interface because surface tension varies with temperature.
For example, U.S. Pat. No. 4,813,851 discloses a device for conveying fluids utilizing the Marangoni type effect. However, the device disclosed in U.S. Pat. No. 4,813,851 does not exhibit the high degree of control required for ink jet printers and other applications. Further, this device is not compatible with standard semiconductor fabrication techniques and thus is difficult to manufacture in small scale.
Accordingly, there is a need for a fluid pump, for use in printers or the like, that is simple in construction and capable of pumping fluid quickly and accurately without boiling the fluid.
An object of the invention is to increase the control accuracy of fluid pumps and print heads utilizing the thermally induced Marangoni type effect.
Another object of the invention is to simplify the construction of fluid pumps and print heads.
Another object of the invention is to impart motion to fluid without the need for moving parts or boiling of the fluid.
Another object of the invention is to utilize standard semiconductor fabrication techniques to manufacture a fluid pump and print head.
Another object of the invention is to improve the performance of ink jet print heads.
The invention achieves these and other objects through a first aspect of the invention which is an ink jet print head comprising a first plate having first and second sides and a first aperture formed therethrough, a second plate having first and second sides and a second aperture formed therethrough, and a spacer coupled to the second side of the first plate and the first side of the second plate to define a secondary fluid passage between the first plate and the second plate. The first aperture and the second aperture are substantially aligned to define an ink passage extending across the secondary fluid passage to thereby define an interface between ink in the ink passage and a secondary fluid in the secondary fluid passage. A first heater is disposed on the first side of the first plate proximate the first aperture, and a second heater is disposed on the first side of the second plate proximate the second aperture. A controller is operatively coupled to the first heater and the second heater to control energization of the first heater and the second heater in a predetermined manner. The interface is heated to create a temperature gradient, and thus a surface tension gradient, to thereby move ink through the ink passage.
A second aspect of the invention is a fluid pump comprising, a first fluid supply mechanism for supplying a primary fluid, a second fluid supply mechanism for supplying a secondary fluid, a first plate having first and second sides and a first aperture formed therethrough, a second plate having first and second sides and a second aperture formed therethrough and a spacer coupled to the second side of the first plate and the first side of the second plate to define a secondary fluid passage between the first plate and the second plate. The first aperture and the second aperture are substantially aligned to define a primary fluid passage extending across the secondary fluid passage. The primary fluid passage is coupled to the primary fluid supply and the secondary fluid passage is coupled to the secondary fluid supply to thereby define an interface between primary fluid in the primary fluid passage and secondary fluid in the secondary fluid passage. A first heater is disposed on said first side of the first plate proximate the first aperture and a second heater is disposed on the first side of the second plate proximate the second aperture. A controller is operatively coupled to the first heater and the second heater to control energization of the first heater and the second heater in a predetermined manner. Fluid is moved through the primary fluid passage due to the Marangoni type effect.